1.Field of the Invention
The present invention relates to the construction and use of a self-contained, opto-mechanical instrument to accurately and rapidly measure linear distances on flat or curved surfaces.
2.Description of the Related Art
Historically, graphic representations of objects, illustrated in proper scale, have been extensively utilized in a wide variety of separate disciplines, such as geology, cartography, aerial photography, medical/industrial imaging, architectural/mechanical drawing, just to name a few. Consequently, the ability to perform precise linear distance measurements on these graphic representations is of significant value.
Various inventions capable of performing linear distance measurements have been described in German Patents 3245864, 3025686, 2751620, Japanese Patents 55-36726, 58-101105, 60-36901, 1-191010, U.S. Pat. No. 4,760,647, 5,067,249, 5,161,313, 3,494,039, British Patent 2200754 and World Patent 85/05175. All of the devices depicted in these patents share several common features including:
1. a rotatable tracking wheel which is employed to trace the distance being measured;
2. mechanical or electronic conversion of tracking wheel movement into numerical values; and
3. device calibration in absolute units of measurement, e.g., inches, centimeters, etc.
In spite of these common design features, however, there are notable differences between the measurement capabilities of these inventions. Furthermore, each of these devices has significant design limitations which negatively impact their use in a variety of different measurement conditions.
These limitations generally fall into the following categories:
1. the integration of the measuring device into a single, portable unit;
2. the basic principle by which these devices perform distance measurements and the device calibration requirements;
3. the ability to select different linear units;
4. the ability to select different linear scales;
5. the complexity of device construction and use; and
6. the ability to perform accurate distance measurement of irregularly shaped lines.
1. Self-Contained Design
Certain of these inventions such as patents 3245864 and 3025686 cannot be considered as single, self-contained units, since the former is intended to operate in conjunction with a separate computer, and the latter requires two separate units (a counter unit and a pulse generator probe) which are made to operate together. On this basis, these patents do not possess the portability and size advantages offered by the self-contained devices.
2. Principles of Measurement
All of the previously identified devices measure distances in a single, absolute linear unit, e.g., inches, centimeters, etc. Of the devices which have multiple unit and scale capabilities, the measured distance (in this absolute unit) is then converted into the specific unit and scale of the illustration being measured. The absolute distance measurement principle adopted by these inventions therefore requires accurate device calibration for this linear unit, and maintenance of such calibration accuracy after prolonged use and under adverse conditions. Variation from this calibration state will necessarily result in inaccurate distance measurements.
3. Linear Unit Selection Patents 2200754, 2751620 and U.S. Pat. No. 4,760,647 only measure and display absolute linear units, e.g., inches or centimeters. Consequently, there are no provisions for the selection of linear units other than those for which the device has been calibrated. Other devices can only function to convert measured linear distances into a specific unit. For example, patents 3025686, U.S. Pat. No. 5,067,249, U.S. Pat. No. 3,494,039, 60-36901 and 1-191010 display the distances between points on a map in miles or kilometers; and 55-36726 displays the unit price per length of raw materials. The application of these devices would therefore be highly restricted to specific distance determinations. Only patents U.S. Pat. No. 5,161,313, 85/05175, and 58-101105 appear to provide a means for selecting different units of measurement. However, even in these latter cases, this selection must be made from a limited list, i.e., the most commonly used units.
4. Linear Scale Selection
The provision for multiple scale selection (within a specified linear unit) differs widely in the prior art. Since patents 2200754, 2751620, U.S. Pat. No. 4,760,647 only function as electronic rulers, the devices cannot directly convert measured distances into different linear scales. Even if the devices are calibrated in the same units as the illustration, such conversion can only be achieved by an independent mathematical calculation. This, in turn, requires additional steps for each distance determination.
As previously mentioned, patents 60-36901 and U.S. Pat. No. 5,067,249 only display distances in miles or kilometers. Furthermore, the use of these devices is additionally restricted by a limited number of selectable scales. Thus, these inventions are unable to measure distances on illustrations which are not of the same scale as the predetermined settings on the devices.
Finally, all of the previously described devices which have the capability to adjust for multiple linear scales shown in patents U.S. Pat. No. 5,161,313, 85/05175, U.S. Pat. No. 3,494,039, 1191010, 58-101105, 3245864 and 3025686 require that the operator know the specific scale of the illustration in absolute units, i.e., miles/inch, kilometers/centimeter, etc. On the other hand, many commonly used graphic representations, e.g. road maps, do not always define the calibration distance of the scale bar in absolute units of measure. In these cases, the operator must first perform separate measurements and calculations before the device can be mechanically or electronically adjusted for the proper illustration scale. Thus, if the calibration scale of the illustration is not represented in absolute units, distance measurement using all of these devices would require multiple operator procedures.
5. Complexity of Design and Use
The devices shown in patents U.S. Pat. No. 5,161,313 and 85/05175 offer the greatest flexibility in measuring different units and scales, but are highly complex in their construction and use. This is due to the fact that this invention measures distances in a single, absolute linear unit, and then mathematically converts measured distance values (in this unit) to other units and scales. Because of this method of measurement, the devices require a complex design to accommodate the manual selection of different units of measurement, as well as the manual entry of numerical scale information. Consequently, this invention must possess multiple function keys, as well as a complete numerical keyboard for data entry. Furthermore, the routine use of this device can be complicated and cumbersome. For example, a distance measurement using this invention would first require the operator to select a unit of measurement, e.g., inches, centimeters, kilometers, etc., from a predetermined and limited number of options. If the device does not possess the particular linear unit desired, e.g., microns, angstroms, etc., the distance measurement could not be readily performed. If unit selection is possible, the operator would then manually enter the numerical scale data, e.g., the number of miles per inch. However, if the absolute scale for instance miles per inch of the illustration is not shown (as is the case with many commonly used maps), the operator would first be required to perform an independent measurement and calculation to generate this scale data before it could be entered into the device. Thus, because of the basic method by which the previous art measures distances, i.e., in absolute units, increases in the device's capability to measure different units and scales, necessarily results in corresponding increases in the device's complexity of construction and use.
6. Distance Measurement of Irregularly Shaped Lines
One important consideration in the present art is a device's capability to measure distances along highly curved lines. This capability has, to a large extent, been determined by the size and shape of the device itself, the diameter of the tracking wheel, and restricted movement of the tracking wheel in a single axis of rotation.
Device size and shape are significant factors, since the ease with which an operator can hold and manipulate the device directly affects his ability to accurately trace a non-linear line. In this regard, the dimensions of a common writing instrument would appear to provide the optimum size and shape characteristics for maximum operator control and manipulation. Although patents U.S. Pat. No. 5,161,313, 85/05175, 58-101105, U.S. Pat. No. 5,067,249, 6036901, and U.S. Pat. No. 3,494,039 seem to meet the criteria for ease of device manipulation, the devices shown in patents U.S. Pat. No. 4,760,647, 2751620, 2200754 and 1-191010 do not suit this description. Consequently, these latter devices could not be readily utilized to precisely trace complex lines.
The tracking wheel diameter is an important consideration for two primary reasons. Firstly, a large diameter can cause visual obstruction of the surface being measured. This is an especially critical factor when short and highly irregular lines are being traced. Secondly, the diameter of the tracking wheel defines the degree of curvature (degrees of arc per unit length) of the wheel circumference. This degree of curvature, in turn, determines the extent of contact between the wheel and the illustration surface. Since accurate tracing can only be achieved if this contact length is smaller than the radius of curvature defined by the line, the devices which possess the smallest wheel diameters, also have the greatest potential for providing the most accurate tracing capabilities. In this connection, however, the mechanical or opto-mechanical methods used by patents U.S. Pat. No. 5,161,313, 85/05175, 58-101105, 5,067,249, 60-36901, and U.S. Pat. No. 3,494,039 severely limit the minimum wheel diameter which can be reasonably employed. Thus, these devices are restricted in their ability to accurately trace highly curved or irregularly shaped lines.
The utilization of a tracking wheel to trace lines can also lead to measurement inaccuracies. Specifically, since a wheel moves about a single axis of rotation, accurate line tracing requires that the wheel be positioned in a particular orientation relative to the line being traced. Consequently, patents 58-101105, U.S. Pat. No. 5,067,249, 60-36901, and U.S. Pat. No. 3,494,039, require that the operator manually align the tracking wheel to this orientation during distance measurements. In practical terms, the ability of the operator to maintain proper wheel orientation would be determined by the considerations previously discussed, i.e., the size and shape of the device, the degree of visual obstruction caused by the tracking wheel, and the extent of contact between the wheel and the illustration surface. Consequently, a device which could be easily manipulated in the hand, and which had a small wheel diameter relative to the curvature of the line, would provide the best potential for tracing highly complex lines.
In an attempt to eliminate this requirement for manual orientation, the devices shown in patents U.S. Pat. No. 5,161,313 and 85/05175 allow the tracking wheel to swivel in a plane perpendicular to the axis of wheel rotation, in a manner analogous to a common caster. Thus, movement of these devices in a specific direction causes the tracking wheel to align itself in the proper orientation relative to the line being traced. Although this design reduces the need for operator manipulation of the device, it also introduces a potential source of measurement inaccuracies. Specifically because of this design, the swiveling action of the caster, itself, will cause rotation of the measuring shaft (50), which, in turn, can result in extraneous pulse generation. This phenomenon could therefore lead to cumulative pulse counting errors during the tracing of irregularly shaped lines, where caster rotation would be the most pronounced.
Furthermore, caster movement of the tracking wheel does not eliminate the need for a small wheel diameter, since the operator must be capable of observing sudden changes in line direction in order to move the device in the appropriate direction.
In short, each of the previously described inventions has certain limitations relative to size, flexibility of unit/scale selection, complexity of design, and measurement accuracy in tracing highly complex lines. These limitations are primarily due to the optical or mechanical methods the devices use to translate tracking wheel movement into distance values, as well as the basic principle by which the devices measure distances in absolute linear units.